Fuel injection pump for internal combustion engines

ABSTRACT

A fuel injection pump for internal combustion engines includes a cylinder sleeve having a first bore and a damping space communicating with the suction space of the pump, and plunger having a smaller diameter portion extending into the bore and displaceable therein to effect delivery of fuel to the internal combustion engine. The fuel injection pump further includes a cam drive for displacing the plunger and a return spring for biasing the plunger to an initial suction position thereof and into engagement with the cam drive. The plunger has a larger diameter portion extendable into the damping space during a delivery stroke for adjusting a volume of the damping space and defining at an end of the delivery stroke, a throttle gap that forms a sole connection between the dampening space and the suction space of the pump.

BACKGROUND OF THE INVENTION

The invention relates to a fuel injection pump including a steppedplunger movable by a cam drive and having a reduced diameter portion forexecuting suction and delivery strokes and an end face for limiting thepump working space. The end face has a damping space connected with thesuction space of the pump and whose volume can be changed. DE-OS3,144,277 has already disclosed a fuel injection pump which, in order toincrease the power by increasing the delivery rate of the pump plunger,has a hydraulic cushioning device in order to compliment the restoringforces required to decelerate the oscillating pump plunger, whichrestoring forces can no longer be produced by the helical springs whichare supposed to hold the pump plunger in contact with the face cams. Theknown hydraulic cushioning device requires a restriction groove on thepump plunger in order to limit the outflow of the fuel from a dampingspace. The formation of the restriction groove on the pump plungerrequires additional and, furthermore, cost-intensive operations sincethe restriction groove must usually be produced by erosion. Furthermore,the braking effect affects the majority of the pump plunger movement,with the result that the driving forces required are higher thannecessary.

SUMMARY OF THE INVENTION

The object of the invention is a fuel injection pump in which a furtherincrease in the velocity of the pump plunger and hence an increase inthe power of the fuel injection pump is possible even though thehydraulic stop does not have an additional compensating groove and thebraking effect occurs only partially in the region of the top deadcentre of the pump plunger. The object of the invention is achieved byproviding a damping face on the plunger portion having a larger diameterand which, at the end of the delivery stroke, is brought into thedamping space and forms a throttle gap forming a connection with thesuction space. It is advantageous to have the braking effect occur onlyin the event of the pump plunger or the camshaft driving the latteractually lifting off from the roller ring at high rotational operatingspeed. It is particularly advantageous here that the delivery strokepressure and the braking pressure on the pump plunger occur temporallyin succession and transverse forces, which can cause the jamming of thepump plunger, are thus avoided.

The present invention both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following detailed description of thepreferred embodiment when read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified partially cross-sectional side view of a fuelinjection pump, according to the invention and FIG. 2 shows in schematicpartially cross-sectional view of a cylinder sleeve of the fuelinjection pump according to the invention, with the pump plunger guidedin the cylinder sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawing shows in FIG. 1, a simplified partially cross-sectional viewof a distributor-type fuel injection pump in which a drive shaft 2 ismounted in a housing 1 and to which a lifting disc 3 arrangedtransversely to the drive shaft 2 is coupled: The lifting disc isprovided with face cams 4 corresponding to the number of cylinders ofthe internal combustion engine which are to be supplied. The bearingsurface of the lifting disc 3 runs on rollers 5, which are held in afixed roller ring 6. At its driving-side end protruding into afuel-filled suction space 26, a pump plunger 9, which slides in a bore 7of a cylinder sleeve 8, has a collar 10, which is fixed to the liftingdisc 3 for rotation therewith. To control the fuel injection quantity, acontrol slide 11 embracing the pump plunger 9 slides on the driving-sidepump plunger portion, in which, for the purpose of controlled dischargeof partial quantities of the fuel delivered, there is arranged atransverse bore 12 which is controlled by the control slide 11, isconnected to a longitudinal bore 13 leading to the end face of the pumpplunger 9 and there opens into a pump working space 14. Engaging thecontrol slide 11 are adjusting means 15, the position of which iscontrolled in known manner by a speed governor. Resting against thecollar 10 of the pump plunger 9 is a guiding blade 16, against which ayoke 18 loaded by at least one return spring 17 is biased. By way ofsimplification, only one return spring 17 is represented, but two ormore return springs 17 are preferably provided. Extending coaxially tothe return spring 17 is a guide pin 19, which is, on the one hand,secured in the housing 1 and, on the other hand, engages through aregister plate 20, the yoke 18, the yoke 18 thus being secured againstrotation. The return spring 17 is supported at one end with a springplate 21 against the housing 1 and, at the other end, against the yoke18, the lifting disc 3 thereby being pressed against the rollers 5. Asthe drive shaft 2 rotates, the pump plunger 9 is rotated concomitantlyin the same way and additionally moved to and fro, the delivery strokebeing effected by the face cams 4 of the lifting disc 13 counter to theaction, of the return spring 17, and the suction stroke is effected bythe stored force of the return spring 17.

The illustrative embodiment represented in FIG. 2 shows a partial viewof a fuel injection pump according to FIG. 1, modified in accordancewith the invention. In this arrangement, the pump plunger 9 is ofstepped design, the part of the pump plunger 9 of smaller diameter beingslidingly guided in the bore 7 of the cylinder sleeve 8. The cylindersleeve 8 has a damping bore 24, which is designed as a damping space,starts from the suction space, faces the part of the pump plunger 9 oflarger diameter, and the axis of which coincides with the axis of thepump plunger 9. The annular front face between the large diameter andthe small diameter of the pump plunger 9 forms a damping face 23. Withinone cycle of movement, the pump plunger 9 assumes a lowermost motionalposition BDC and an uppermost motional position TDC. During a deliverystroke movement, the damping face 23 of the pump plunger 9 in contactwith the face cams 4 approaches the forward limitation of the dampingspace 22 in TDC but for a small dimension which is less than 1 mm. If,in the case of high velocity, the inertial force of the pump plunger 9exceeds the contact force of the return spring 17, the positiveengagement between pump plunger 9 and face cam 4 is lost. As a result,shortly after BDC, the damping face 23 of the pump plunger 9 can enterthe damping space 23, thereby forming an annular gap 25 between thecircumferential surface of the part of the pump plunger 9 of largerdiameter and the damping bore 24 bounding the damping space, which gapthen forms the only connection between the damping space 22 and a fuelinjection pump suction space 26 leading as a relief space. Thethrottling of the fuel enclosed in the damping space 22 leads toformation of a hydraulic spring, the return force of which is oppositeto the movement of the pump plunger 9 and, after the delivery strokemovement of the pump plunger 9, assists, in the same direction, theactuating force of the return spring 17. To modify the return force ordamping, different or additional throttling connections of the dampingspace 22 with the suction space 26 or other accumulating spaces can beprovided in order to reduce the maximum pressure.

The functional sequence described results in the following sequence ofactions. In TDC the outer contour of the face cam 4 has the smallestradius, with the consequence that the positively following pump plunger9 here undergoes the greatest decelerations. In the illustrativeembodiment described, a highly accelerated pump plunger 9 lifts off fromthe face cam 4 before TDC but, due to the damped braking, is quicklylimited in its free flight shortly after TDC and rapidly guided backonto the face cam 4, the efficiency of the cam drive thereby beingincreased. The transverse forces caused by the delivery stroke pressuredue to the torsion of the drive shaft 2 and to the displacements of thecam drive can cause pointwise wear which leads to sticking of the pumpplunger 9. The separation, described above, of the positive engagementbetween the pump plunger 9 and face cam 4 prevents the influence oftransverse force on the pump plunger before TDC; the bearing wear of thepump plunger 9 is thus largely circumvented. By virtue of the catchingof the oscillating pump plunger 9 with a of hydraulic additional forcein a manner according to the invention, the illustrative embodimentdescribed permits, in combination with lower susceptibility to wear,higher delivery rates or driving speeds of the fuel injection pump, orhigher numbers of strokes of the pump plunger per revolution for thesame delivery quantity, this resulting in an increase in the power ofthe fuel injection pump.

While the invention has been illustrated and described as embodied in afuel injection pump, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:
 1. A fuel injection pump for internal combustion engines,comprising a suction space having a first bore and a damping spacealigned to said bore and communicating with said suction space; aplunger having a smaller diameter portion extending into said first boreenclosing there a pump work chamber and displaceable therein to effectdelivery of fuel out of the pump work chamber to the internal combustionengine, cam drive means for displacing said plunger; and spring meansfor biasing said plunger to an initial suction position thereof and intoengagement with said cam drive means, said plunger having a largerdiameter portion that adjoins to said smaller diameter portion adaptedto pass into said damping space forming a throttling gap between itsjacket face and the adjacent wall of said damping space that forms asole connection between said damping space and said suction space;wherein said larger diameter portion only passes into said damping spaceconsequent to a further movement of the plunger against said springmeans after having reached its uppermost displacement in following a camlobe.
 2. A fuel injection pump as defined in claim 1; and furthercomprising a damping bore, said damping space being radially limited bysaid damping bore, said damping bore and said first bore of saidcylindrical sleeve having same axes.
 3. A fuel injection pump as definedin claim 1, wherein said damping face is formed by an annular facebetween said smaller diameter portion and said larger diameter portionof said plunger.
 4. A fuel injection pump as defined in claim 1; andfurther comprising a damping bore which radially limits said dampingspace, said gap being formed by a movement play between a surface ofsaid larger diameter portion of said plunger and said damping bore.